Ratio changing brake actuating system



June 8, 1943. w. R. FREEMAN V RATIO CHANGING BRAKE ACTUATING SYSTEM Filed May 2, 1941 om i F AA 2 u. v mm nlAggz mm 0N MN MW.

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ATTORNEY class is permitted when the indicates a master is provided with through associated with its head surface a sealing cup 8. -,A pedal 9 actuates the piston by means of an arm it. The master cylinder device :just de-,-'

Patented June 8, 1943 RATIO CHANGING BRAKE ACTUATING SYSTEM Walter R.'Freeman, Clayton, Md, minor to Wagner Electricflorporation, St. Louis, Mo., a

corporation oi Delaware Application May 2, 194;, Serial No. 391,452

Claims.

My invention relates to brake actuating means and more particularly to an improved hydraulic brake actuating system.

One of the objects of my'invention is to pro- 'duce an improved hydraulic brake actuating system in which is embodied means for'changing the ratio between the hydraulic pressure created by a manually-controlled -master cylinder and 'the pressure efiective in actuating the brake after said master cylinder has'developed a predetermined pressure.

Another and more specific object of my invention is to produce a hydraulically-actuated provided with a sealing cup 20. The forward end of this cylinder is in direct communication with the branch conduit H by a conduit 2 I. The piston I8 is normally biased to aretracted position by a spring 22 and when in this position it uncovers a porthole 22 which is in direct com- .munication with the branch conduit l3, previously referred to, by a conduit 24. The piston I9 is of the spool type providing an annular chamber 25 and this chamber is in constant com munication with conduit 24 by way of a passage 2 to thus maintain a body of. fluid behind the head oi the piston. By means of this body of braking system in which standard parts can be so employed and readily associated with each other that a change in fluid pressure ratio can be obtained during brake application and without any noticeable effect on the foot of theoperator during actuation of the pedal-operated master cylinder.

Still another object of my invention is to produce a hydraulic brake. actuating system of the is so arranged that free' contraction and" expansion of the liquid due to v system is inoperative.

Other objects of my invention will become apparent from the following description taken in connection with the accompanyins ..drawing in which the single figure is a schematic view'of a hydraulic brake actuating system, the main parts thereof being shown in section.

changes in temperature.

permitted to by-pass the packing cup 2'. Pasdescribed which is simple and eflicient in j operation, economical to manufacture and which fluid sub-atmospheric pressure wiil be prevented from developing in the cylinder ahead of the piston during retracting of said piston asfluid is sages 21 are provided in the head .of theplston to facilitate this bar-passing.

Attached to the rear end of cylinder Iris 9.

. second cylinder 2! of larger diameter and within this c'ylinderis a piston 28 held in retracted position by a spring II. The piston 28 is 'connected to actuate the piston is by a rod II and a conduit 32'places cylinder. 28 in directicom- -munication with the branch conduit II. 1

Interposed in the branch conduit .l2 at a point between its juncture with conduit H and the juncture of conduit 2| therewith. is a check valve 38. This valve comprises a casing 34 provided with a valve'seat 351 with which cooperates a valve element it normally biased to a seated Referring to the drawing in detail, numeral "1 cylinder device comprising a cylinder 2, a piston 3. and a reservoir I. The I piston is normally held in retracted position by a spring 5 and when in this position it. uncovers a.

porthole .8 whereby the cylinder will be in direct two-way communication with the reservoir in order to permit contraction and expansion of the fluiddue to temperature changes. The piston 3 passages "I and has scribed and its operation-are well known.

A conduit ll leads from the forward end of cylinder 2-and connected thereto are branch conduits l2 and II, the latter being connected to position by a light spring 31. The check .valve permits fluid to flow through the branch conduit l2 from the master cylinder but prevents any reverse flow.

Referring now to the operation of the braking system .Just described, the parts will be in the positions shownflwhen the system is inoperative and said system includingreservoir 4 is-fllled with a suitable'iiquid. Under these conditions contraction and expansion of the fluid due to temperature changes is permitted since reservoir I is in communication with all the conduits, cyl-' inders and brake actuating fluid motors because portholes. i and 28 will he uncovered.

fluid motors I by other branch conduits I 5, said fluid motors actuating the shoes 16 of brake assemblies l'l.

Associated with the conduits i2 and I3 is a cylinder l8 inv which isreciprocable a piston I! when it is desired to apply the brakes, pedal I is depressed. This will result in porthole] being I closed and the fluid ahead of-the piston 8 placed under pressure. The fluid under pressure will be free to flow to ie nuid motors u by way'otconduit l2 and through check valve 33 or byway of conduits I: and 2l,portho1e a, cylinder u. and

conduit II. If piston I is moved Slowly, the

flow may be through the porthole 23. However, if

l2 and check valve 33 were not employed, the

system would not function as efliciently as desired; If valve 33 were eliminated and piston 3 moved rapidly, the small porthole 23 would so restrict flow of fluid that a sufliclent pressure would be built up to move pistons 29 and I9 and cut off the porthole before thedesired amount of fluid was transmitted to the fluid motors to take up the slack and apply the brakes. With valve 33 fluid can be placed in thefluid motors very rapidly by the master cylinder. Fluid under pressure developed by the master cylinder also flows to cylinder 28 and is eflective on piston 29 since said cylinder is in direct communication with the master cylinder by conduit 32. The fluid pressure developed by the master cylinder will thus cause operation of the fluid motors of the brake assemblies and apply the brakes. Piston 29 will not be operated during this initial operation of the fluid motors due to the strength of spring 39.

When the pressure developed by the master cylinder'reaches such a value that spring 30 will be compressed, piston 29 will move to the left, as viewed in the figure, and cause a like movement of piston i9. When piston 19 has moved sumciently to cut off porthole 23, it will begin to develop pressure and this pressure, which is,

greater than the pressure being developed by .the master cylinder due to the master cylinder piston being of a larger diameter than piston l9, will be effective only in the fluid motor H as the check valve 36 will be held closed.

It is thus seen that when passage 23 is cut off I by 'movementpf piston l9, there will be a change in ratio between the pressure being developed by themain master cylinder and the pressure effective in the fluid motors H for actuating the brakes. Prior to this change, the fluid pressures were of the same value since the main master cylinder was in direct communication with the fluid motors l4. By means of the change in ratio the brakes can be applied with a greater force by the same manual effort than would be possible if the master cylinder were directly connected with the fluid motors II for two-way communication at all times. I

In practice it has been found desirable to have piston 3 of the main master cylinder and piston 29 substantially the same size. In the drawing the mainmaster cylinder and its piston 3 are shown on a smaller scale than cylinders l8 and 23 and their pistons l9 and 29. Preferably, themaster cylinder piston for a particular brake system is larger than that used wherein no change in ratio is provided.

The braking system results in the brakesbeing initially applied by a fairly large displacement offluid due to the fact that the main master cylinder piston is quite large. After the brakes have become applied and all slack has been taken up, the brakes will be applied additionally by the piston of smaller diameter. Thus it is seen that there is a mechanical advantage obtained which is very desirable. I

When it is desired to release the brakes, the pedal is released, thus relieving the pressure be- .hind piston 29. The springs 30 and 20 will now returnthe pistons 29 and 19 to their inoperative positions and fluid from the fluid motors will be returned by the action of the usual brake shoe return springs. The fluid motors M will now again be in communication with reservoir 4 of the master cylinder. Thus if there-is any excess fluid in the system, it can return to the reservoir. If, during the return movement of piston l9, there should be sub-atmospheric pressure developed ahead of this piston, fluid will by-pass piston l9 from chamber 25 by way of passages 26 and around the. packing cup 20. This bypassed fluid will prevent air from being drawn into the system. Also, if during the release of the brakes there. should be a tendency for subatmospheric pressure to develop ahead of the master cylinder piston 3, fluid will by-pass this piston by way of passages l and around packing cup 8.

It is to' be particularly noted in the braking.

system just described that standard parts only are employed, thereby permitting the system to be manufactured at a very low cost. Also, the

arrangement is such that there will be no noticeable efiect on the operator's foot when the change in ratio takes place. At the time or the changeover, the fluid pressure in the entire system is equal and corresponds to that being developed by the master cylinder. Whenpiston I9 is moved to cut off porthole 23 and cause a higher fluid pressure to be effective in the fluid motors ll than that being developed by the master cylinder, there will be a change in pressure until the new ratios are established. This change may be somewhat gradual if the piston '3 is being moved slowly or it may be quite rapid if said, piston is being moved rapidly. The spring 30 also is effective in making a smooth change as it must be compressed.

Since the change-over unit comprising the cylinders l3 and 28 is a separate unit from the master cylinder, it may be positioned at any place desired. The same is true of the check valve 33. These separate units thus facilitate the installation of the braking system as no one place need be found where all of the units, including the master cylinder, will fit.

Being aware of the possibility of modifications in the particular structure herein described without departing from the fundamental principles of my invention, I do not intend that its scope be limited except as set forth by the appended claims.

Having fully described my invention, what I 'claim as new and desire to secureby Letters Patent of the United States is:

1. In braking apparatus, a brake, a fluid motor for actuating the brake, a manually-controlled master cylinder comprising a cylinder, a piston, a reservoir, and means permitting the reservoir to have two-way communication with the cylinder ahead of the piston only when the piston is in retracted position, a second cylinder, a piston therein, -conduit means for connecting the cylinder of the master cylinder and the second cylinder to thefluid motor, means for directly moving the piston of the second cylinder solely by fluid pressure being developed by continued movement of the piston of the master cylinder, said'last named means embodying means for caus ng the pressure developed by the piston of the second cylinder to be greater than the pressure developed by the master cylinder, means for causing the I fluid pressure developed by the piston in the second cylinder to be effective only in actuating the fluid motor, and means for placing the second cylinder and the fluid motor in two-way communication with the cylinder of the master cylinder and its reservoir only when the second piston and the piston of the master cylinder are in retracted position. i

2. In braking apparatus, a brake, a fluid motor for catuating the brake, a manually-controlled master cylinder comprising a cylinder, a piston, a reservoir and means permitting the reservoir to have two-way communication with the cylinder ahead of the piston only when the piston is in retracted position, a second cylinder, a piston therein, said last named piston being of smaller diameter than the master cylinder piston, conduit means for'connecting the cylinder of the master cylinder and the second cylinder to the fluid motor, check valve means associated with the conduit means for preventing at all times return flow of fluid under pressure through the conduit means from the fluid motor to the mascontrolled by themovement of the piston so as to pressure developed by the master cylinder, means for causing the fluid pressure developed by the piston in the'second cylinder to be effective only in actuating the fluid motor, and means for placconduit means for connecting the master cylinder device to the fluid motor, means operable when a predetermined pressure is developed by the master cylinder for trapping fluid in the fluid motor and for causing said master cylinder by continued operation to directly apply solely by means of the fluid pressure being developel a greater pressure to the trapped fluid than that being de-,

veloped by the master cylinder, said means comprising a normally closed check valve in said conduit means, a by-pass conduit around said check valve, and valve means for closing said bypass conduit only after the fluid pressure developed by the master cylinder reaches the predetermined value. I

4. In braking apparatus, a brake, a fluid motor for actuating the brake, a master cylinder device, conduit means for connecting the master cylinder device to the fluid motor, means operable when a predetermined pressure is developed by the master cylinder for trapping fluid in the fluid motor and for causing said master cylinder to apply a greater pressure to the trapped fluid than that being developed by the master cylinder, said means comprising two cylinders of difl-erent size, the larger of which is connected to the master cylinder and the smaller of which is connected to the fluid motor, connected pistons in said cylinders, spring means preventing movement of the pistons until a predetermined pressure is developed in the master cylinder, a normally closed I for actuating the brake, a manually-controlled master cylinder device, a separate. cylinder, a piston therein, conduit means for connecting the master cylinder device and the cylinder to the permit said two-way communication only when the piston is in inoperative position, and means movable solely by the increasing fluid pressure developed by the continued operation of the master cylinder for directly actuating the piston and causing fluid pressure developed thereby to act only on the fluid motor.

6. In braking apparatus, a brake, a fluid motor for actuating the brake, a manually-controlled 'master cylinder device, a separate cylinder, a

piston therein, conduit means for connecting the master cylinder device and the cylinder to the fluid motor, normally closed check valve means associated wtih the conduit means for preventing at all times return flow of fluid-under pressure through the conduit means from the fluid motor to the master cylinder device, by-pass means around the check valve for permitting two-way communication between the master cylinder and fluid motor, said by-passing means comprising valve means controlled by the movement of the piston so as to permit said two-way communication only when the piston is in inoperative position, a second cylinder oflarger diameter than the'first cylinder, a piston therein, a connection between the last named piston and first named piston, and conduit means for placing the second cylinder in communication with the master cylinder.

7. In braking apparatus, a brake, a fluid motor for actuating the brake, a manually-controlled master cylinder device, a cylinder, a piston therein, conduit means for connecting the master cylinder device and the cylinder to the fluid motor,

check valve means associated with the conduit means for preventing at all times return flow of fluid under pressure through the conduit means from the fluid motor to the master cylinder device, by-pass means around the check valve for permitting two-way communication between the master cylinder and fluid motor andgcomprising aporthole uncovered by the piston when in inoperative-position so as to permit said two-way communication only when the piston is in said position, and means movable solely by the -'increasing fluid pressure developed by the continued operation of the master cylinder for directly actuating the piston and causing fluid pressure developed thereby to act only on the fluid motor.

8. In braking apparatus, a brake, a fluid motorfor actuating the brake, a pedal-operated master cylinder, conduit means connecting the master cylinder to the fluid motor, a check valve for preventing return flow of fluid through said conduit means at all times, a cylinder connected to the fluid motor, a piston therein, said cylinder being provided with a porthole which is uncovered by the piston when in. retracted position, conduit means connecting the porthole with the master cylinder, a second cylinder of larger diameter than the first cylinder, a piston therein, conduit means for placing the second cylinder in communication with the master cylinder, and spring means for biasing the two pistons to inoperative position.

,9. In braking apparatus, a brake, a fluid motor for applying the brake,.a master cylinder device comprising a cylinder and a piston, a second cylv inder of smaller diameter than the cylinder of conduit means for preventing at all times fluid under pressurefrom flowing through the conduit means from the second cylinder and fluid motor to th cylinder of the master cylinder device, conduit means connecting the porthole to the cylinder the master cylinder and permitting twoway communication between the master cylinder device and the 'fluid motor when the piston in' th second cylinder is in retracted position, and

mea'ns for moving the piston of the second cylinder solely and directly by increased fluid pressure developed by the mastercylinder device.

10. In braking apparatus, a brake, a fluid motor for applying the brake, a master cylinder device comprising a cylinder and a piston, a second cylinder of smaller diameter than the cylinder of the? master cylinder device, a piston in said second cylinder, said second cylinder being provided with a porthole which is uncovered by the piston therein when in retracted position, conduit means connecting'th'e cylinder of the master cylinder device and the second cylinder to the fluid motor, a one-way valvejn said conduit means for preventing at all times fluid under pressure from flowing through the conduit means from the second cylinder and fluid motor to the cylinder of the master, cylinder device, conduit means connecting the porthole to, the cylinder oi" the master cylinder and permitting two-way communication between the master cylinder de' vice and the fluid motor when the piston in the second cylinder is in retracted position, and means for moving the. pistonot the second cylinder only when the fluid pressure developed by the master cylinder device is a predetermined value, said last named means comprising a third cylinder, a piston therein and connected to the piston in the second cylinder, means for placing the third cylinder in communication with the master cylinder, and a spring acting to oppose movement of the piston in the third cylinder by pressure developed by the mastercylinder.

WALTER R. FREEMAN. 

